ROOF MOUNTED NATURAL COOLED DYNAMIC BRAKING RESISTOR

Abstract

1. A roof mounted natural cooled dynamic braking resistor comprising a plurality of resistor elements stacked in parallel path in a housing, each of said resistor elements comprising of at least one resistor strip, and each said resistor elements being located with interstitial spaces therebetween to ensure easy flow of atmospheric air for cooling.

SATISH NATH SHARMA and CHANDER PRAKASH SHARMA, both Indian citizens, of 10 E Industrial Area, Govindpura, Bhopal 462 023, Madhya Pradesh, INDIA
The following specification particularly describes the nature of the invention and the manner in which it is to be performed.

GRANTED
12-10-2004

ROOF MOUNTED NATURAL COOLED DYNAMIC BRAKING RESISTOR Field of the invention
The present invention relates to a novel roof mounted natural cooled dynamic braking resistor. More particularly, the present invention relates to a novel dynamic braking resistor for locomotives. Background of the invention
An important unit of a locomotive system is the braking arrangement provided thereon. Safety in locomotive travel has become an important area of focus due to the large number of railroad related accidents all over the world. In India, the problem is compounded by the fact that the railway system is one of the largest in the world and is responsible for hauling more freight and passengers annually than any other railway system. Another feature affecting the safety of rail travel in India is that in most areas, the rail tracks are unprotected enabling easy access to human and animal population across the tracks. Due to this, it is essential that railroad locomotives be provided with an efficient braking system that is long lasting and economical.
Prior art braking systems in locomotives in use in India comprise of mechanical braking arrangements and include conventional features such as brake shoes and brake blocks.
Modern day locomotives are primarily electric locomotives that generally are fed direct electrical power from overhead cables lining the entire route of the train. An alternative method of supply of electric power in locomotives is self-generated power by burning carbonaceous fuels in the locomotive cab to generate the power required throughout the train. In both the above cases, the motive power is electricity. The electricity generated powers electric motors

generally referred to as traction motors, which in turn provide motive power to the wheels of the cab through a simple gear arrangement.
In prior art systems, the application of brakes in the locomotive cab results in the stopping of the supply of electricity to the armature of the traction motor. However, the stator, which is the non-mobile part of the traction motor, continues to be fed with electricity. The moving rotor in the motor generates electricity as a principle and the electric flux in the stator acts upon the rotating armature to produce a braking effect. However, during the time taken for the braking effect to act, the rotating armature continues to generate electricity, which is converted into heat by feeding it to resistors. The high levels of heat energy generated require to be dissipated quickly so as to avoid overheating of the braking system.
In view of the above, prior art braking systems are provided with an independent cooling system to ensure quick dissipation of heat. However, the cooling system of such prior art systems is subject to failure. Also, prior art systems result in high wear and tear of the braking components requiring servicing and/or replacement of the components almost every six months.
US Patent 6,036,284 disclose a modular locomotive brake control unit with electropneumatic modules, each including removable pneumatic elements as a unit in a manifold. However, the focus of the disclosure in the above-referred US Patent is on braking control and there is no disclosure or reference to prevention of wear and tear or dissipation of the heat energy generated during braking operations.
US Patent 6,035,250 discloses a locomotive brake control unit with dynamic brake interlock. The invention of the above-referred US Patent is
generally for computer controlled railroad-braking equipment and not for manually operated braking systems.
US Patent 5, 813,730 discloses a retrofit air distribution apparatus for a
locomotive braking system which is configured to act as an interface with an
electronic braking control device. The disclosure does not provide any information
for control of a manual braking operation.
US Patent 4, 352,049 discloses a brake control apparatus and method for transit vehicles generally with a brake effort request P signal indicating the desired brake effort and with the receptivity of the power supply line determining how much electric braking energy is regenerated to the power supply line and how much is dissipated in the dynamic braking resistors.
Prior art systems suffer from the disadvantages of not providing a fail-safe system for dissipation of heat energy generated during braking operations and therefore result in wear and tear of the braking systems. The prior art systems also require constant monitoring to ensure that the resistors and the cooling systems are functioning effectively. On an average, prior art systems require replacement and/or servicing every six months and are therefore also more expensive.
Mechanical braking systems of the prior art are not only subject to fast wear and tear but are also not completely fail safe and can result in wheel skidding and consequent derailment when the brakes are applied in an emergency.
It is therefore imperative to devise a system for braking of locomotives that is inexpensive, fail-safe, generates greater confidence in the locomotive driver and is also efficient.

Objects of the invention
It is therefore an object of the invention to provide a dynamic braking resistor with improved efficiency that is also cost effective.
It is another object of the invention to provide a fail-safe dynamic braking
resistor that ensures quick dissipation of heat energy generated during braking
operations.
It is a further object of the invention to provide a dynamic braking resistor that eliminates the need for an expensive and cumbersome cooling system used in the prior art. Summary of the invention
Accordingly the present invention provides a roof mounted natural cooled dynamic braking resistor comprising a plurality of resistor elements stacked in parallel path in a housing, each of said resistor elements comprising of at least one resistor strip, and each said resistor elements being located with interstitial spaces therebetween to ensure easy flow of atmospheric air for cooling.
In one embodiment of the invention, the resistor strip comprises of corrugations.
In a further embodiment of the invention, the housing comprises a frame, wherein the said plurality of resistor elements is stacked in a parallel path.
In another embodiment of the invention, each of said plurality of resistor elements is provided with a spring element in order to prevent sagging.
In a further embodiment of the invention, the dynamic braking resistor is connected to the traction motor of the locomotive by means of a bus bar.
In another embodiment of the invention, the spacing between the resistor elements is between 50 to 60 mm.

The invention also relates to a strip useful for the making of a resistor element, said strip comprising of an elongated piece of material being provided with evenly spaced corrugations, said corrugations winding spirally from one end of the strip to the opposite end thereof.
The invention also provides a method for the manufacture of a corrugated resistor strip useful in the making of a resistor element, said method comprising taking at least three element strips of equal lengths, placing the said element strips in parallel and corrugating the said element strips in a manner as herein described to form a single corrugated resistor strip.
In another embodiment of the invention, the resistor element comprises of at least three resistor strips with even spacing there between. Brief description of the accompanying drawings
Figure 1 is a side representation of the roof mounted dynamic braking resistor of the invention.
Figure 2 is a top representation of the roof mounted dynamic braking resistor of the invention.
Figure 3 is a graph of electrical resistivity and its temperature dependence.
Figure 4 discloses the placement of the resistor of the invention on the locomotive cab.
Figure 5 is a representation of the corrugated resistor strip of the invention.
Figure 6 discloses the position of the thermocouples for the temperature rise test.

detailed description of the invention
The dynamic braking resistor of the invention eliminates the presence of
cooling systems such as blowers or blower motors present in the prior art. As a
result, the failure factor in dynamic braking is minimized since the apparatus of
the invention relies on atmospheric dissipation of heat and not on an artificial
cooling system.
The dynamic braking resistor can comprise of any number of resistor elements stacked preferably in parallel so as to ensure that maximum benefit of the air currents in atmosphere are availed. Each resistor element comprises preferably at least one resistor strip made of Nickel chrome 60:15. The optimum size of the strip is 43.0 X 0.56 mm and length is about .18.11 metres. The total preferred volume of the resistance strip for Indian conditions for the complete unit is 43 x 0.56 meters x 3 coils in parallel x 12 nos. and is normally about 0.015645 Cu. Metres. The preferred resistance of the resistor is 0.584 Ohms.
The resistor strip is preferably corrugated to ensure complete circulation of air and least resistance to heat dissipation. The enlarged surface area thus available on the corrugated strip enables greater dissipation of heat generated during braking operation in a rnore timely manner and thus ensures that the equipment wear and tear and stress due to heat are minimized substantially.
The length of the corrugated strip is normally about 0.67 metres as compared to prior art strip length of one meter. The entire resistor is housed in a corrosion and weather proof housing comprising preferably a steel frame so as to ensure that rain, moisture or coastal salty air does not affect the frame itself. The hole pitch of the frame where the insulator is mounted is done so as to ensure that the gap between the element strips as mounted is at least 10 to 15 mm.

The resistor strips are manufactured by taking three or more element strips of equal lengths (i.e. plane length of element: 18.11 meters length) for three parallel paths while keeping the element strips in parallel one above the other. The elements are then placed in a element forming machine to convert the plane element to corrugated form. The element forming machine consists of two pressing tools. The teeth of both the pressing tools are same i.e. pressing toolare placed in such a way that gap between the teeth of both pressing tool are equal-to thickness of the three strip for converting plane shape to corrugated shape and the machine is motor operated (motor is of very low RPM). The element strips are placed in the machine and the strip is pressed by pressing tools to convert the same in corrugated form. The elements are fed from one side and rolled out in corrugated form on other side. Adjustment screw are present to adjust the depth of pressing if the element pressing is found more. The adjustment screws are present over the element forming machine.
The element strips are converted from 18.11 meter plane to 12.13 meters corrugation (i.e. 1 meter plane length corrugated to 0.67 meter corrugation therefore, 18.11 meter plane length converted to 12.13 meter corrugation).
The element strips are converted to corrugated form because of the very limited space over the roof of locomotive for dynamic braking resistor, so to achieve the resistance value and better heat dissipation. The above length i.e. 12.13 meters corrugated is required to achieve the resistance value i.e. 0.584 ohms and for better heat dissipation. I.e. actual length to accommodate the resistor element strip in given space is 12.13 meters length corrugation.
The present invention will now be described with reference to several
performance and characteristics tests that were carried out to determine the

eficiency and performance levels of the apparatus. It must be understood that the test results given below are only illustrative of the invention and should not be read as limiting the nature and scope of the invention. TEMPERATURE RISE TEST:
A temperature rise test was conducted on the apparatus of the invention mounted on a standard railway locomotive. Before conducting the test, the resistance value at ambient temperature of 33°C was recorded. The values are given in Table I below. The temperature was recorded at different positions by connecting 20 numbers of thermocouples on the dynamic braking resistor of the invention. Table I:
Check on rated resistance values at ambient temperature and corrected to 20°C:

Dielectric test
After the temperature rise test, dielectric test was conducted by applying 4.00 KV between the element and earth for 1 minute, 3.00 KV between the element and the tie rod for 1 minute; and 3.25 KV applied between the tie rod and earth for I minute respectively. It was observed that the dynamic braking

resistor of the invention withstood the voltages at all the points. The insulation resistance value before and after the high voltage being applied was found to be more than 200 megaohms. No deformity or sagging or breakage or abnormality was observed in the resistance elements and the insulators after the tests. Rain tests
The roof mounted dynamic braking resistor of the invention was heated to about 700°C (the maximum operating temperature) and water sprayed on the unit at an angle of 45 degrees from vertical plane with an output of 3mm/minute for 5 minutes. The element assemblies were then tested for dielectric test as follows:
3.00 KV between the element and earth; 2.00 KV between the element and the tie rod 2.25 Kv between the tie rod and earth.
It was observed that the insulation resistance value before and after the HV was more than 100 megaohms. No abnormality was observed in the resistance material after the tests. Hygroscopic tests
A hygroscopic test was conducted by keeping the dynamic braking resistor of the invention in a closed chamber for 24 hours while maintaining relative

Humidity of 95% at 25°C. After removing the unit from the chamber the following dielectric tests were conducted within 5 minutes: 3.00 KV between the element and earth; 2.00 KV between the element and the tie rod; 2.25 KV between the tie rod and earth.
It was observed that the insulation resistance value before and after the HV was more than 100 megaohms. No obnormality was observed in the resistance material after the tests.
The test results of the dynamic braking resistor of the invention in operation to examine its efficiency in terms of braking and reduction of speed are given in Table i, ii, iii and iv below, i) Test for maintaining a particular speed by leading loco while DBR was in circuit.
Following observation were recorded

686°C — 700 13 11.53
90 600°C — 600 8 11.55
80 550°C — 600 9
80 550°C — 600 9 12.20
iv. Trial on reducing speed from 40 Kmph to 10 Kmph and maintaining the same for
longer duration:-
On returning back from Bina to Bhopal DBR loco was leading loco. At 40 Kmph DBR was put in circuit and speed brought down from 40 Kmph to 10 Kmph. After that 10 Kmph speed was maintained for 20 minutes at a stretch. Following observations were made:-

Traction current in pushing loco was 400 Amps ¥ Traction current in pushing loco was 700 Amps Observation was made using air brake
From 90 Kmph to 50 Kmph; Time Taken: 1 Minutes 20 seconds; Loco 23579 with 23440 trailing loco
Note: Communication between the drivers of leading & trailing locos was made through walkie-talkie

In Figure 1 of the accompanying drawings, the components are made of materials as indicated below:

WE CLAIM:
1. A roof mounted natural cooled dynamic braking resistor comprising a plurality of resistor elements stacked in parallel path in a housing, each of said resistor elements comprising of at least one resistor strip, and each said resistor elements being located with interstitial spaces therebetween to ensure easy flow of atmospheric air for cooling.
2. A dynamic braking resistor as claimed in claim 1 wherein the resistor strip comprises of corrugations.
3. A dynamic braking resistor as claimed in claim 1 wherein the housing comprises a frame, wherein the said plurality of resistor elements are stacked in a parallel path.
4. A dynamic braking resistor as claimed in claim 1 wherein each of said plurality of resistor elements is provided with a spring element in order to prevent sagging.
5. A dynamic braking resistor as claimed in claim 1 wherein the dynamic braking resistor is connected to the traction motor of the locomotive by means of a bus bar.
6. A dynamic braking resistor as claimed in claim 1 wherein the spacing between the resistor elements is between 50 to 60mm.
7. A dynamic braking resistor as claimed in claim 1 the resistor element comprises of at least three resistor strips with even spacing therebetween.

8. A strip useful for the making of a resistor element, said strip comprising of an elongated piece of material being provided with evenly spaced corrugations, said corrugations winding spirally from one end of the strip to the opposite end thereof.
9. A method for the manufacture of a corrugated resistor strip useful in the making of a
resistor element, said method comprising taking at least three element strips of equal
lengths, placing the said element strips in parallel and corrugating the said element
strips in a manner as herein described to form a single corrugated resistor strip.
10. A roof mounted natural cooled dynamic braking resistor substantially as described
herein before and as illustrated in the accompanying drawings.
11. A strip useful for the making of a resistor element substantially as described herein
before and as illustrated in the accompanying drawings.
12. A method for the manufacture of a corrugated resistor strip useful in the making of s
resistor element substantially as described herein before and as illustrated in the
accompanying drawings.
Dated this the 26th day of May, 2000
G. NATARAJ Of Subramaniam, Nataraj & Associates Attorneys for the Applicants